U.S. patent number 6,788,737 [Application Number 10/070,459] was granted by the patent office on 2004-09-07 for communication terminal apparatus, base station apparatus and communication method.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Katsuhiko Hiramatsu, Kenichi Miyoshi.
United States Patent |
6,788,737 |
Miyoshi , et al. |
September 7, 2004 |
Communication terminal apparatus, base station apparatus and
communication method
Abstract
PL demodulation section 203 demodulates pilot signals of a
received signal. SIR detection section 205 detects the reception
quality of the demodulated pilot signals. fd detection section 206
detects a Doppler frequency using the demodulated pilot signals.
Requested modulation method deciding section 207 decides a
modulation method to be requested to the base station using the
reception quality of pilot signals and the detected Doppler
frequency. Command generation section 208 generates a command
corresponding to the decided modulation method. Adaptive
demodulation section 204 performs demodulation processing on the
received signal using the demodulation method corresponding to the
modulation method decided by requested modulation method deciding
section 207. This makes it possible to maintain good reception
quality even in a fading environment.
Inventors: |
Miyoshi; Kenichi (Yokohama,
JP), Hiramatsu; Katsuhiko (Yokosuka, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
18718991 |
Appl.
No.: |
10/070,459 |
Filed: |
March 7, 2002 |
PCT
Filed: |
July 19, 2001 |
PCT No.: |
PCT/JP01/06284 |
PCT
Pub. No.: |
WO02/09377 |
PCT
Pub. Date: |
January 31, 2002 |
Foreign Application Priority Data
|
|
|
|
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Jul 26, 2000 [JP] |
|
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2000-225171 |
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Current U.S.
Class: |
375/219; 370/468;
375/222; 375/261; 375/377 |
Current CPC
Class: |
H04L
1/0015 (20130101); H04L 1/0003 (20130101); H04L
1/0025 (20130101) |
Current International
Class: |
H04L
1/00 (20060101); H04L 005/16 () |
Field of
Search: |
;375/219,222,261,377
;370/468 ;706/14 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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06242225 |
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Sep 1994 |
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JP |
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07250116 |
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Sep 1995 |
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JP |
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09200282 |
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Jul 1997 |
|
JP |
|
10041876 |
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Feb 1998 |
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JP |
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10056420 |
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Feb 1998 |
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JP |
|
10093650 |
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Apr 1998 |
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JP |
|
10247955 |
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Sep 1998 |
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JP |
|
11220774 |
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Aug 1999 |
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JP |
|
11331936 |
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Nov 1999 |
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JP |
|
9750197 |
|
Dec 1997 |
|
WO |
|
Other References
"HDR Air Interface Physical Layer", Qualcomm Incorporated, Mar. 28,
2000. .
"High Speed Downlink Packet Access", Motorola Network Solutions
Sector, May, 2000..
|
Primary Examiner: Liu; Shuwang
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher, LLP
Claims
What is claimed is:
1. A communication terminal apparatus comprising: a receiver that
receives a radio signal from a base station apparatus; a reception
quality detector that detects a reception quality of said received
signal; a selector that selects a modulation method applicable to
the radio signal from a plurality of modulation methods of varying
transmission rates based on a scale of the detected reception
quality in comparison to a threshold for said reception quality; a
transmitter that transmits a command to request the selected
modulation method to the base station apparatus; and a Doppler
frequency detector that detects a Doppler frequency from said
received signal, wherein said selector sets a greater threshold in
response to an increase in the detected Doppler frequency.
2. The communication terminal apparatus according to claim 1,
wherein: said radio signal comprises a pilot section and a data
section that are time multiplexed; said reception quality is a
reception quality of the pilot section; said Doppler frequency
detector detects said Doppler frequency from the pilot section of
said radio signal; said selector sets said greater threshold in
response to an increase in the detected Doppler frequency from the
pilot section of said radio signal; said modulation method is
applicable to the data section of the radio signal; and said
selector selects said modulation method applicable to the data
section of the radio signal taking into account a characteristic
difference that arises from fading between the pilot section and
the data section.
3. A base station apparatus that transmits a radio signal to a
communication terminal apparatus, said communication terminal
apparatus receiving the radio signal, detecting a reception quality
of the received signal, selecting a modulation method applicable to
the radio signal from a plurality of modulation methods of varying
transmission rates in accordance with the detected reception
quality, and transmitting a command to request the selected
modulation method to the base station apparatus, said base station
apparatus comprising: a receiver that receives said command; a
changer that changes the modulation method requested by the command
with another modulation method; a modulator that modulates the
radio signal by said another modulation method; a transmitter that
transmits the modulated signal to the communication terminal
apparatus; and a detector that detects a Doppler frequency from a
received signal, wherein said changer changes the modulation method
requested by the command with said another modulation method of a
lower transmission rate in response to an increase in the detected
Doppler frequency.
4. The base station according to claim 3, wherein: said radio
signal comprises a pilot section and a data section that are time
multiplexed; said communication terminal apparatus detects the
reception quality of the pilot section and selects a modulation
method applicable to the data section of the radio signal from the
plurality of modulation methods of varying transmission rates in
accordance with the detected reception quality; said detector
detects said Doppler frequency from the pilot section of the
received signal; and said changer changes the modulation method
requested by said command with a modulation method of a lower
transmission rate in response to an increase in the detected
Doppler frequency taking into account a characteristic difference
that arises from fading between the pilot section and the data
section.
Description
TECHNICAL FIELD
The present invention relates to an adaptive modulation method used
in a digital mobile unit communication system.
BACKGROUND ART
For a digital mobile unit communication system, there are proposals
about an adaptive modulation method such as HDR (High Data Rate) in
recent years. A communication using a conventional HDR will be
explained with reference to FIG. 1 below. FIG. 1 is a schematic
view showing a downlink slot format used for communications using
an HDR.
First, a communication terminal apparatus demodulates pilot (PL1
and PL2) sections of a received signal and detects an SIR. The
communication terminal apparatus then decides a modulation method
that allows the reception quality of data sections to satisfy a
required quality based on the detected SIR and decides the
modulation method to be requested to a base station apparatus.
A specific example of a method of deciding the modulation method
will be explained with reference to FIG. 2. FIG. 2 is a schematic
view showing a method of deciding a modulation method in a
communication using a conventional HDR.
In FIG. 2, when the SIR of a pilot section is lower than threshold
1, even if the communication terminal apparatus receives data to
which 16 QAM or 64 QAM is applied, the reception quality of the
data section does not satisfy a desired BER (10.sup.-3). Therefore,
the communication terminal apparatus selects QPSK as the modulation
method to be requested to the base station apparatus.
Furthermore, when the SIR of the pilot section is between threshold
1 and threshold 2, even if the communication terminal apparatus
receives data to which 16 QAM is applied, the reception quality of
the data section can satisfy the desired BER. Thus, the
communication terminal apparatus selects 16 QAM as the modulation
method to be requested to the base station apparatus. Furthermore,
when the SIR of the pilot section is higher than threshold 2, even
if the communication terminal apparatus receives data to which 64
QAM is applied, the reception quality of the data section can
satisfy the desired BER. Thus, the communication terminal apparatus
selects 64 QAM as the modulation method to be requested to the base
station apparatus. These are specific examples of the method of
deciding the modulation method.
Then, the communication terminal apparatus notifies the decided
modulation method to the base station apparatus.
On the other hand, the base station apparatus performs scheduling
based on the modulation method notified from each communication
terminal apparatus and sends data to which the modulation method
notified from this communication terminal apparatus is applied to
the communication terminal apparatus decided by the scheduling.
However, movements of a communication terminal apparatus cause
fading in a mobile unit communication system. In a fading
environment, even if there is no change in the reception quality of
a pilot section (pilot signal), a Doppler frequency of fading (fd)
may cause the reception quality of the data section (received data)
to deteriorate, which results in a large difference between the
reception quality of the pilot section and the reception quality of
the data section.
More specifically, since the time zone occupied by a pilot section
in a slot is short as is apparent from FIG. 1, the reception
quality of the pilot section in the communication terminal
apparatus is favorable even in a fading environment. On the other
hand, since the time zone occupied by a data section in a slot is
long, in a fading environment, a phase rotation occurs in the data
section received by the communication terminal apparatus due to the
fading. This causes the reception quality of the data section in
the communication terminal apparatus to deteriorate, which results
in a large difference between the reception quality of the pilot
section and the reception quality of the data section (that is, the
reception quality of the data section falls below the reception
quality of the pilot section in a fading environment).
As a result, when the communication terminal apparatus decides a
modulation method to be requested to the base station apparatus
based on the reception quality measured in pilot section, the
reception quality of the data section in the communication terminal
apparatus fails to satisfy the required quality.
As shown above, the conventional adaptive modulation method has a
problem that the quality of received data in a communication
terminal apparatus falls below the desired quality in a fading
environment, having difficulty in performing highly efficient and
high quality data communications.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a communication
terminal apparatus capable of maintaining favorable reception
quality even in a fading environment.
This object is attained by deciding a modulation method applied to
an information signal based on the reception quality of a known
reference signal and a Doppler frequency.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view showing a downlink slot format used for
a communication using an HDR;
FIG. 2 is a schematic view showing a method of deciding a
modulation method in a communication using a conventional HDR;
FIG. 3 is a block diagram showing a configuration of a base station
apparatus according to Embodiment 1 of the present invention;
FIG. 4 is a block diagram showing a configuration of a
communication terminal apparatus according to Embodiment 1
above;
FIG. 5 is a block diagram showing a configuration of an fd
detection section in the communication terminal apparatus according
to Embodiment 1 above;
FIG. 6 is a schematic view showing a method of detecting an fd by
the fd detection section in the communication terminal apparatus
according to Embodiment 1 above;
FIG. 7 is a schematic view showing an example of a method of
deciding a modulation method at a requested modulation method
deciding section in the communication terminal apparatus according
to Embodiment 1 above;
FIG. 8 is a block diagram showing a configuration of a base station
apparatus according to Embodiment 2 of the present invention;
and
FIG. 9 is a block diagram showing a configuration of a
communication terminal apparatus according to Embodiment 2 of the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference now to the attached drawings, embodiments of the
present invention will be explained in detail below.
Embodiment 1
This embodiment will describe a case where a modulation method is
decided based on a Doppler frequency detected by a communication
terminal apparatus. FIG. 3 is a block diagram showing a
configuration of a base station apparatus according to Embodiment 1
of the present invention. Suppose the base station apparatus shown
in FIG. 3 performs transmission to a communication terminal
apparatus using the slot format shown in FIG. 1, for example.
In FIG. 3, reception RF section 102 performs predetermined radio
reception processing such as frequency conversion on a signal
received via antenna 101 (received signal). Command demodulation
section 103 demodulates a command sent from the communication
terminal apparatus by applying demodulation processing to the
received signal subjected to the radio reception processing.
Adaptive modulation section 104 applies adaptive modulation to
transmission data using the modulation method decided according to
the command demodulated by command demodulation section 103.
Transmission RF section 105 generates a transmission signal by
time-multiplexing pilot signals (pilot signal 1 "PL1" and pilot
signal 2 "PL2") subjected to predetermined modulation and
transmission data subjected to adaptive modulation, applies
predetermined radio transmission processing such as frequency
conversion to the transmission signal generated and sends the
transmission signal subjected to the radio transmission processing
via antenna 101.
FIG. 4 is a block diagram showing a configuration of a
communication terminal apparatus according to Embodiment 1 of the
present invention. In FIG. 4, reception RF section 202 applies
predetermined radio reception processing such as frequency
conversion to a signal received via antenna 201 (received
signal).
Adaptive demodulation section 204 demodulates data sections using
the received signal subjected to the radio reception processing. PL
demodulation section 203 demodulates pilot signals using the
received signal subjected to the radio reception processing. SIR
detection section 205 detects reception quality (e.g., SIR) using
the pilot signals demodulated by PL demodulation section 203. fd
detection section 206 detects fd (Doppler frequency) using the
pilot signals demodulated by PL demodulation section 203.
Requested modulation method deciding section 207 decides a
modulation method (e.g., QPSK, 16 QAM, 64 QAM) to be requested to
the base station apparatus using the reception quality of the pilot
signals detected by SIR detection section 205 and the fd detected
by fd detection section 206. The method of deciding the modulation
method will be described later.
Command generation section 208 generates a command corresponding to
the modulation method decided by requested modulation method
deciding section 207. Modulation section 209 modulates the command
generated by command generation section 208. Transmission RF
section 210 applies predetermined radio transmission processing
such as frequency conversion to the command modulated by modulation
section 209 and sends the command subjected to the radio
transmission processing via antenna 201.
FIG. 5 is a block diagram showing a configuration of fd detection
section 206 in the communication terminal apparatus according to
Embodiment 1 of the present invention. In FIG. 5, of the pilot
signals demodulated by PL demodulation section 203, "PL1" is output
to PL1 channel estimation section 301 and "PL2" is output to PL2
channel estimation section 302.
PL1 channel estimation section 301 performs channel estimation on
demodulated "PL1". PL2 channel estimation section 302 performs
channel estimation on demodulated "PL2".
Angle difference detection section 303 calculates angle difference
.theta. between both channel estimation results using the channel
estimation result from PL1 channel estimation section 301 and the
channel estimation result from PL2 channel estimation section
302.
fd calculation section 304 is fed information indicating a time
difference (hereinafter referred to as "time difference
information" )between "PL1" and "PL2" in the slot frame shown in
FIG. 1. This fd calculation section 304 detects a Doppler frequency
using the time difference information and angle difference .theta.
from angle difference detection section 303.
Then, operations of the communication terminal apparatus and the
base station apparatus having the above-described configurations
will be explained. First, in the base station apparatus shown in
FIG. 3, transmission RF section 105 generates a transmission signal
by time-multiplexing pilot signals ("PL1" and "PL2") subjected to
predetermined modulation and transmission data subjected to
adaptive modulation as shown in FIG. 1. The transmission data
subjected to adaptive modulation will be described in further
detail later. The transmission signal generated is subjected to
predetermined radio transmission processing and sent via antenna
101.
The signal sent from the base station apparatus is received by the
communication terminal apparatus shown in FIG. 4 via antenna 201.
In FIG. 4, the signal received via antenna 201 (received signal) is
subjected to predetermined radio reception processing by reception
RF section 202. The signals corresponding to the data sections (see
FIG. 1) of the received signal subjected to the radio reception
processing are output to adaptive demodulation section 204, while
the signals corresponding to the pilot signals of the received
signal subjected to the radio reception processing are output to PL
demodulation section 203.
PL demodulation section 203 performs demodulation processing on the
received signal from reception RF section 202. In this way, pilot
signal 1 "PL1" and pilot signal 2 "PL2" are demodulated.
Demodulated "PL1" and "PL2" are output to SIR detection section 205
and fd detection section 206.
SIR detection section 205 detects the reception quality using "PL1"
and "PL2" demodulated by PL demodulation section 203. The reception
quality detected is output to requested modulation method deciding
section 207.
fd detection section 206 detects an fd (Doppler frequency) using
"PL1" and "PL2" demodulated by PL demodulation section 203. A
specific example of fd detection will be explained with reference
to FIG. 5 and FIG. 6. FIG. 6 is a schematic view showing a method
of detecting an fd by fd detection section 206 in the communication
terminal apparatus according to Embodiment 1 of the present
invention.
According to FIG. 5, "PL1" demodulated by PL demodulation section
203 is input to PL1 channel estimation section 301 and "PL2"
demodulated by PL demodulation section 203 is input to PL2 channel
estimation section 302.
PL1 channel estimation section 301 performs channel estimation on
demodulated "PL1". PL2 channel estimation section 302 performs
channel estimation on demodulated "PL2". The channel estimation
results by PL1 channel estimation section 301 and PL2 channel
estimation section 302 are output to angle difference detection
section 303.
Angle difference detection section 303 calculates angle difference
.theta. between the "PL1" channel estimation result and the "PL2"
channel estimation result as shown in FIG. 4. The calculated angle
difference .theta. is output to fd calculation section 304.
fd calculation section 304 detects a fading variation using angle
difference .theta. calculated by angle difference detection section
303 and time difference information and calculates a Doppler
frequency (fd). The calculated fd is output to requested modulation
method deciding section 207.
Requested modulation method deciding section 207 decides a
modulation method to be requested to the base station apparatus
using the reception quality of the pilot signals detected by SIR
detection section 205 and the fd detected by fd detection section
206. As the modulation method, the one which allows the reception
quality of the data sections of this communication terminal
apparatus to satisfy required quality and is fastest as well is
decided. A specific method for deciding a requested modulation
method will be further explained with reference to FIG. 7
below.
FIG. 7 is a schematic view showing an example of a method of
deciding a modulation method by requested modulation method
deciding section 207 in the communication terminal apparatus
according to Embodiment 1 of the present invention. FIG. 7 shows a
relationship between the reception quality (SIR) of pilot signals
and the quality of received data (error rate characteristics: BER)
in the cases of, for example, a high fd and a low fd, respectively
at the communication terminal apparatus when the base station
apparatus applies a QPSK system, 16 QAM system and 64 QAM system to
transmission data.
As is apparent from FIG. 7, there is a difference in the
characteristic of received data in the cases of a high fd and low
fd even if the communication terminal apparatus receives pilot
signals with equal quality. That is, the characteristic of received
data in the case of a high fd deteriorates compared to the
characteristic of received data in the case of a low fd. Thus, when
the fd changes, the characteristic of received data changes a great
deal even if the reception quality of pilot signals remains
unchanged.
Thus, this embodiment decides a modulation method using thresholds
provided according to fd. That is, this embodiment provides
threshold 1 and threshold 2 for a high fd and low fd,
respectively.
When fd is high, in the case where the reception quality of a pilot
signal is lower than threshold 1 (high fd), a QPSK modulation
method is selected, when the reception quality of a pilot signal is
between threshold 1 (high fd) and threshold 2 (high fd), a 16 QAM
modulation method is selected and when the reception quality of a
pilot signal is higher than threshold 2 (high fd), a 64 QAM
modulation method is selected. On the contrary, in the case where
fd is low, when the reception quality of a pilot signal is lower
than threshold 1 (low fd), a QPSK modulation method is selected,
when the reception quality of a pilot signal is between threshold 1
(low fd) and threshold 2 (low fd), a 16 QAM modulation method is
selected and when the reception quality of a pilot signal is higher
than threshold 2 (low fd), a 64 QAM modulation method is
selected.
Here, the above-described thresholds can be set as follows. That
is, characteristics of received data (received data when QPSK, 16
QAM or 64 QAM, etc. is applied) with respect to the reception
quality of pilot signals are obtained in the cases of a high fd and
low fd respectively. Furthermore, the minimum required reception
quality of pilot signals so that the characteristic of received
data meets the desired quality when a 16 QAM modulation method is
applied is set to threshold 1 and the minimum required reception
quality of pilot signals so that the characteristic of received
data meets the desired quality when a 64 QAM modulation method is
applied is set to threshold 2 in the cases of a high fd and low fd
respectively.
This embodiment has described the case where the modulation method
is decided according to the cases of a high fd and low fd
respectively, but the present invention is also applicable to a
case where the modulation method is decided according to fd of
three or more types. Thresholds can be set using the
above-described method in such a case, too.
Selecting a modulation method in this way is equivalent to
selecting the modulation method by estimating characteristic
differences between pilot signals and received data using the
detected Doppler frequency and taking into account these
characteristic differences. This is a specific method of deciding
the modulation method by requested modulation method deciding
section 207.
The modulation method decided in this way is notified to command
generation section 208. Command generation section 208 generates a
command corresponding to the modulation method decided by requested
modulation method deciding section 207. The command generated by
command generation section 208 is modulated by modulation section
209, subjected to predetermined radio transmission processing by
transmission RF section 210 and then sent via antenna 201. An
operation of adaptive modulation section 204 will be described
later.
A signal sent from the communication terminal apparatus is received
by the base station apparatus shown in FIG. 1 via antenna 101. In
FIG. 1, the signal received via antenna 101 (received signal) is
subjected to predetermined radio reception processing by reception
RF section 102. The received signal subjected to radio reception
processing is demodulated by command demodulation section 103. The
command sent from the communication terminal apparatus is
demodulated in this way. The demodulated command is output to
adaptive modulation section 104.
Adaptive modulation section 104 performs adaptive modulation on the
data to be transmitted to the communication terminal apparatus
using the modulation method decided according to the command from
command demodulation section 103. The transmission data subjected
to adaptive modulation is output to transmission RF section 105.
Hereafter, as described above, transmission RF section 105
time-multiplexes pilot signals subjected to predetermined
modulation and transmission data subjected to adaptive modulation
to generate a transmission signal, performs predetermined radio
transmission processing on the transmission signal generated and
transmits the signal via antenna 101.
The signal transmitted from the base station apparatus is received
by the communication terminal apparatus shown in FIG. 2 via antenna
201 as described above. As shown above, of the received signal
subjected to radio reception processing by reception RF section
202, signals corresponding to the data sections (see FIG. 1) are
output to adaptive demodulation section 204, while of the received
signal subjected to radio reception processing, signals
corresponding to pilot signals are output to PL demodulation
section 203. The operation of PL demodulation section 203 is as
described above.
Adaptive demodulation section 204 performs demodulation processing
on the received signal subjected to radio reception processing by
reception RF section 202 according to the demodulation method
corresponding to the modulation method used by adaptive modulation
section 104 at the base station apparatus shown in FIG. 3. Received
data is obtained in this way.
Thus, this embodiment detects a Doppler frequency using pilot
signals, estimates the reception quality of the received data in a
fading environment using the detected Doppler frequency and the
reception quality of the pilot signals and decides a modulation
method to be requested to the base station apparatus based on the
estimated reception quality of the received data. That is, this
embodiment estimates characteristic differences between pilot
signals and received data using the detected Doppler frequency and
decides the modulation method to be requested to the base station
apparatus taking into account these characteristic differences.
In this way, this embodiment can reliably decide the modulation
method which is fastest and at the same time allows the quality of
received data at the communication terminal apparatus to satisfy
required quality even in a fading environment, and can thereby
provide high quality and highly efficient data communications.
For the sake of simplicity, this embodiment has described the case,
as an example, where one communication terminal apparatus decides a
modulation method based on a Doppler frequency, notifies the
decided modulation method to the base station apparatus and the
base station apparatus sends transmission data obtained by applying
the modulation method notified by this communication terminal
apparatus to the communication terminal apparatus. However, the
present invention is also applicable to cases where transmission
data is sent to a plurality of communication terminal
apparatuses.
That is, the present invention is also applicable to a case where a
plurality of communication terminal apparatuses decides a
modulation method likewise, notifies the decided modulation method
to a base station apparatus, while the base station apparatus
decides (schedules) the communication terminal apparatus that
transmits data based on the modulation method notified from each
communication terminal apparatus and sends the transmission data to
the communication terminal apparatus according to the scheduling.
In this case, it goes without saying that when the base station
apparatus sends the transmission data to a communication terminal
apparatus, the base station apparatus applies the modulation method
notified by this communication terminal apparatus to the
transmission data.
Furthermore, this embodiment has described the case, as an example,
where a downlink slot format shown in FIG. 1 is used, but the
present invention is not limited to this and the present invention
can naturally apply any slot format other than the one shown in
FIG. 1. More specifically, an applicable slot format corresponds to
a slot format obtained by time-multiplexing data sections (sections
for transmitting information signals) and pilot sections (sections
for transmitting known reference signals). A time difference
between pilot sections and the number of pilot sections per slot
are not limited to particular ones as far as they allow detection
of fd.
Embodiment 2
This embodiment will describe a case where the base station
apparatus detects a Doppler frequency using a received signal and
decides a modulation method applicable to data to be transmitted to
the communication terminal apparatus based on the detected Doppler
frequency and a modulation method notified from the communication
terminal apparatus.
In above-described Embodiment 1, the communication terminal
apparatus detects fd. However, fd is only decided by the moving
speed of the communication terminal apparatus, and therefore the
base station apparatus detects fd of an uplink signal and can
regard it as fd of a downlink signal. Thus, in this embodiment, it
is not the communication terminal apparatus but the base station
apparatus that detects fd.
FIG. 8 is a block diagram showing a configuration of a base station
apparatus according to Embodiment 2 of the present invention. The
same components in FIG. 8 as those in Embodiment 1 (FIG. 3) are
assigned the same reference numerals as those in FIG. 3 and
detailed explanations thereof are omitted.
In FIG. 8, fd detection section 601 detects fd using a received
signal subjected to radio reception processing from reception RF
section 102. fd detection section 601 can use any signal sent from
the communication terminal apparatus as a received signal to detect
fd.
Correction section 602 recognizes the modulation method notified
from the communication terminal apparatus using a command
demodulated by command demodulation section 103 and decides a
modulation method applicable to transmission data for the
communication terminal apparatus using the recognized modulation
method and the fd detected by fd detection section 601. Adaptive
modulation section 603 performs adaptive modulation on the
transmission data using the modulation method decided by correction
section 602.
FIG. 9 is a block diagram showing a configuration of a
communication terminal apparatus according to Embodiment 2 of the
present invention. The same components in FIG. 9 as those in
Embodiment 1 (FIG. 4) are assigned the same reference numerals as
those in FIG. 4 and detailed explanations thereof are omitted.
In FIG. 9, requested modulation method deciding section 701 decides
a modulation method to be requested to the base station apparatus
using the reception quality of pilot signals detected by SIR
detection section 205.
Adaptive demodulation section 702 has a configuration similar to
that of adaptive demodulation section 204 in Embodiment 1 (FIG. 4)
except that adaptive demodulation section 702 performs demodulation
processing using the demodulation method corresponding to the
modulation method used for adaptive modulation section 603 in FIG.
8.
Then, operations of the communication terminal apparatus and base
station apparatus having the above-described configurations will be
explained. The same operations in this embodiment as those in
Embodiment 1 are omitted. First, in the communication terminal
apparatus shown in FIG. 9, requested modulation method deciding
section 701 decides a modulation method to be requested to the base
station apparatus using the reception quality of pilot signals
detected by SIR detection section 205. As the modulation method,
the one which allows the reception quality of data sections at this
communication terminal apparatus to satisfy required quality and is
fastest as well is decided. The decided modulation method is
notified to command generation section 208 as described above.
Then, at the base station apparatus shown in FIG. 8, a received
signal subjected to radio reception processing by reception RF
section 102 is output to command demodulation section 103 and fd
detection section 601. Command demodulation section 103 performs
the processing explained in Embodiment 1 and demodulates the
command sent from the communication terminal apparatus.
fd detection section 601 detects fd using the received signal
subjected to radio reception processing. As a specific fd detection
method, it is possible to use the same method for fd detection
section 206 in Embodiment 1. The detected fd is notified to
correction section 602.
Correction section 602 corrects the command demodulated by command
demodulation section 103 (that is, modulation method notified from
the communication terminal apparatus) based on the detected fd.
More specifically, in the case of a high fd, even if the modulation
method notified from the communication terminal apparatus is 16
QAM, a modulation method whose transmission rate is one step lower
than 16 QAM is set as the modulation method applicable to
transmission data for this communication terminal apparatus. It is
also possible to set a modulation method two or more steps lower
than the modulation method notified from the communication terminal
apparatus according to the magnitude of fd. The modulation method
set by correction section 602 is notified to adaptive modulation
section 603.
Adaptive modulation section 603 performs adaptive modulation on
transmission data to be sent to the communication terminal
apparatus using the modulation method set by correction section
602. The transmission data subjected to adaptive modulation is
output to transmission RF section 105 as explained in Embodiment
1.
After this, at the communication terminal apparatus shown in FIG.
9, adaptive demodulation section 702 performs demodulation
processing on the received signal subjected to radio reception
processing by reception RF section 202 according to the
demodulation method corresponding to the modulation method used by
adaptive modulation section 603 at the base station apparatus shown
in FIG. 8. Received data is obtained in this way.
Thus, according to this embodiment, the base station apparatus
detects a Doppler frequency using a signal transmitted from the
communication terminal apparatus, changes the modulation method
(candidate) (to a modulation method with a lower transmission rate)
decided by the communication terminal apparatus solely based on the
reception quality of pilot signals according to the detected
Doppler frequency and sends transmission data to which the changed
modulation method is applied to the communication terminal
apparatus. That is, the base station apparatus estimates a
characteristic difference between pilot signals and received data
at the communication terminal apparatus using the detected Doppler
frequency and decides the modulation method to be applied to
transmission data for the communication terminal apparatus taking
this estimated difference into account.
This makes it possible to reliably decide a modulation method which
is fastest and at the same time allows the quality of received data
at the communication terminal apparatus to satisfy desired quality,
thereby allowing high quality and highly efficient data
communications. Furthermore, this eliminates the need for a circuit
to calculate a Doppler frequency at the communication terminal
apparatus and thereby simplifies the circuit configuration of the
communication terminal apparatus. As a result, it is possible to
reduce power consumption at the communication terminal apparatus
and reduce the size of the communication terminal apparatus.
Embodiment 1 above has described the case where the communication
terminal apparatus detects fd using two pilot signals which are
time-multiplexed with the transmission data and sent by the base
station apparatus. However, the communication terminal apparatus
can also detect fd using any signals (may also be signals other
than pilot signals) sent by the base station apparatus. For
example, the communication terminal apparatus can also detect fd
using pilot signals (one or a plurality of pilot signals)
code-multiplexed or time-multiplexed with the transmission data by
the base station apparatus.
Likewise, Embodiment 2 has described the case where the base
station apparatus detects fd using a signal sent from the
communication terminal apparatus, but the base station apparatus
can also detect fd using any signals code-multiplexed or
time-multiplexed with the transmission data, etc. by the
communication terminal apparatus.
As is apparent from the above-described explanations, the present
invention decides a modulation method to be applied to information
signals based on the reception quality of a known reference signal
and a Doppler frequency, and can thereby provide a communication
terminal apparatus capable of maintaining good reception quality
even in a fading environment.
This application is based on the Japanese Patent Application No.
2000-225171 filed on Jul. 26, 2000, entire content of which is
expressly incorporated by reference herein.
Industrial Applicability
The present invention is ideally applicable to a digital mobile
unit communication system.
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